Proposed research involves the further investigation of several aspects of the cell bioenergetics of a salt-dependent microorganism, Halobacterium halobium. Three major efforts may be listed: 1) elucidation of the coupling stoichiometry of cellular energy (i.e., chemical gradient of sodium and/or an electrical potential difference) to the cotransport of sodium and amino acids; 2) characterization of the mechanisms by which the primary energy form, an electrochemical sodium gradient, in these organisms is created; and 3) investigation into the relationship of the newly-described light-driven sodium pump to the energy-transducing enzyme (ATPase) responsible for controlling the synthesis and degradation of ATP, the biological currency. Specific emphasis is centered on the nature and affinity of the sodium and amino acid binding and release steps under objective 1). The observed shift in stoichiometry of sodium: amino acid transport in response to a change in the nature of the driving force is of extreme interest. An understanding of this crucial feature is the prime objective of the proposed research. The stoichiometry shift will be investigated for the various amino acid transport groups in the presence or absence of a second homologous or heterologous amino acid. The primary objective under item 2) is to obtain a description of the exact nature of the light-energy transduction (photon absorption) into chemical and electrical energy. Possible intermediates in this process (e.g., protons or electrons) imply that the sodium pump may be functionally separable into at least a photon-absorbing and a sodium translocating component. The 3) objective will deal with the nature of photophosphorylation by an ATPase that may be functionally linked with the light-driven sodium pump. Research will consider the roles of both the sodium and proton chemical and electrochemical gradients in the photophosphorylation. Established methods of adjusting ion gradients, separation of the gradients into their electrical and chemical components using membrane envelope vesicles are amenable here. Isolation followed by functional reconstitution may be possible and will be attempted.